A MMW-based wireless network is directed to a wireless network which uses MMW as a carrier to carry information. It mainly refers to an Ultra Dense Network, UDN which is generally regarded as the next generation communication system following the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) system. The UDN is expected to provide data rates up to 10 Gbit/s and even higher, which might meet user requirements for increasing data traffic.
Compared with technologies operating at lower frequencies, however, MMW which operates at higher frequencies may suffer more severe signal attenuation which thus results in very short transmission distances. With respect to ANs (access nodes) and/or UEs (user equipments) in the MMW-based wireless network, high gain beamforming with a large number of antenna elements is therefore mandatory which can enhance intensity of beams or increase transmission distances, thus ensuring beam coverage (or signal coverage).
Due to usage of beamforming, multiple beams in different directions that carry the same information (e.g. beacon signals, system signals, other signals which can be used for cell discovery, various measurement, information broadcast, synchronization between an AN and a UE, and so on) would be transmitted by an AN to cover a whole desired coverage area (e.g. a circular coverage area) if the AN want to broadcast system information and the like. Transmission of the multiple beams by an AN may be referred to a beacon sweeping (of course, it can be referred to a system signal sweeping, a reference signal sweeping, and so on) and can be performed periodically.
FIG. 1 illustrates an exemplary beacon sweeping performed by an AN according to the prior art. The AN has a circular coverage area and will transmit N partially overlapped beams to cover the coverage area during a period of time (e.g. during Ta). FIG. 2 illustrates a time diagram which shows that transmission of the N beams can be performed periodically and their period is Ta, for example. As can be seen from FIG. 2, within each period Ta, N same beams will be transmitted to cover the whole desired coverage area. The beams are nearly the same at all times. Moreover, if a large area is desired to be covered, N will be a big number. This means a large number of beams will be transmitted frequently. However, frequent transmission of the large number of beams means a large overhead (e.g. a large number of beams need to be transmitted by an AN, a lot of power will be consumed, etc), and may not be always necessary depending on various factors such as population density, coverage required actually, surroundings, and so on.